Four main categories of contaminants are present in drinking water supplies: organic, microbiological, inorganic, and particulate matter.
It is well known in the field of water purification that particulate matter can be removed by strainers, fibrous filters, sand beds, granular anthracite packed beds, and diatomaceous earth filters. However, the current invention is specifically concerned with the removal of the first three categories of contaminants, which will typically penetrate particulate filters, namely organic and inorganic dissolved compounds and microbes.
Organic compounds present in today's water systems include hydrocarbons such as humic, fulvic and tannic acids, petroleum products such as oil, gasoline and kerosine, and volatile organic compounds ("VOCs") such as chloroform, benzene, aldehydes, trichloroethylene, toluene, chloral, chloroethane and vinyl chloride. Other organic compounds include pesticides, herbicides, algaecides, dioxin, phenols, polychlorinated biphenyls ("PCBs"), hydrogen sulfide, alcohols, ammonia and urea.
Organic compounds are currently removed from drinking water by the use of granulated activated carbon ("GAC") and/or diffused or packed-tower aeration. Although GAC, like other carbonous sorbents, may remove VOCs, it is not effective in removing other harmful contaminants such as hydrogen sulfide and ammonia. It is also well known that activated carbon tends to form densely packed beds, particularly in their finely divided state where they are most efficient. These densely packed beds experience pressure loss, inhibiting the flow of liquid. Thus, it is difficult to utilize GAC in performing continuous filtration of liquid streams. Microbial contaminants also commonly exist in water systems, especially in rural areas, which are without the benefit of chlorination. These contaminants include bacteria, algae, fungi, yeast and viruses. Microbiological contaminants are currently removed with ceramic filters, chemical disinfection or ultraviolet ("UV") irradiation.
With respect to the removal of microbial contaminants, packed beds of sufficiently small particles are helpful in reducing microbial contamination in water. Cholera, for example, was eradicated in New York in the 1800's in part by the institution of sand bed filters throughout the State. Granular sorbent beds may also remove bacteria and algae from water; however, they are much more conducive to biological colonization than sand because of their irregular, jagged surfaces which provide secure, stagnant crevices for microbe attachment and growth. Further, as a result of their sorption of certain other contaminants such as sulfates and humic acid, the granular sorbent beds may also provide nutrients to the attached microbes. The presence of nutrients fosters the biological growth of the microbes. Microbes, such as anaerobic bacteria, in turn, produce sulfide gases. Therefore, using granulated sorbents alone may increase the biological contamination of the water supply as well as the increase the production of undesirable, noxious sulfide gases. Further, utilizing such a filter system would require an additional disinfecting step such as UV irradiation.
Biological growth is retarded in the present invention by the presence of silica hydrogel sorbent. This sorbent creates an acidic condition in its aqueous environs, especially during non-flowing periods. Trace quantities of aluminum ions from the activated alumina sorbent, as well as copper, zinc, brass, manganese and silver, also retard biological growth.
Inorganic contaminants dissolved in water systems include radicals such as chlorine, fluorine, nitrates, sulfates and phosphates as well as metals such as mercury, lead, arsenic, copper, zinc, chromium and iron. Inorganic compounds are usually removed from drinking water through the processes of reverse osmosis ("RO"), deionization ("DI"), distillation, electrodialysis, and crystallization (or freezing).
In the prior art, U.S. Pat. No. 4,238,334, Halbfoster, is directed to a filter bed for removing impurities from liquids, such as removing chlorine from an aqueous suspension, comprising a mixture of treated fibrous filter aid material and an active particulate material. The active particulate material is indicated to be selected from the group consisting of organic polymeric absorbent, zeolite, bentonite, zirconium oxide, zirconium phosphate, activated alumina, ferrous sulfide, activated carbon and diatomaceous earth. No discussion is directed to potable water.
U.S. Pat. No. 4,081,365, Eugene B. White et al., is directed to a method and a apparatus for the treatment of sewage and waste materials in accordance with a specific process. In the process, a regeneration step may be utilized whereby a tertiary treatment apparatus is reactivated through a wet-oxidation process, employing air and water that has been heated to a desired temperature, the water being supplied from a reservoir and then heated. The sorbent bed is described as containing minerals, such as red flint, on top of which is disposed an adsorption layer comprising a hydraulic mix of activated carbon and quartz. The '365 patent indicated that the effluent may conceivably be used as potable water, with the addition of chlorine, clearly indicating, then, that the water is not suitable or potable water in that tertiary treatment. Further, chlorination of water may result in the production of potentially harmful chlorinated hydrocarbons such as chloroform and trihalomethanes ("THMs") by the reaction of chlorine with humic materials.
U.S. Pat. No. 4,661,256, Johnson, is directed to the removal of trace quantities of hydrocarbonaceous compounds from an aqueous stream, by adsorbing hydrocarbon impurities onto a regenerable adsorbent. According to the patent, the aqueous stream is contacted with an adsorbent such as a molecular sieve, amorphous silica-alumina gel, activated carbon, activated alumina, silica gel, or clay. However, no discussion of a use of a mixture of such adsorbents appears in the '256 patent.
Clearly, heretofore there has not existed a single filtration means that is capable of treating water containing any one or more of a variety of contaminants, including organic, inorganic and microbial contaminants, to render said water potable. A device capable of treating such a wide variety of contaminants is especially desirable for use in applications in which the nature of the contaminants and the quantity thereof may vary daily, or hourly, as is true for closed environment water purification applications, as exist for underwater exploration vessels and the like. A similar need also exists for use in point of use filtration in the vicinity of Superfund sites, that may cause the effluent to have any of a wide variety of contaminants, that may frequently change, depending upon subterranean water flow, surface water flow, and the like.
Thus, there exists a need for a device and method that are capable of providing potable water by effectively removing substantially all organic, inorganic and microbial components in a one step process. Such a device should also prevent any increased biological contamination of the water during the filtration process.